This goes over basic and obscure information regarding Rainy Season. Additionally, this guide contains spoilers.
Guide to Basics
To earn this achievement, you must take a bath, which can only be accomplished at night. You can find the bathtub in the room next to the laundry room, which is near the entrance. Once it is night time, you just need to interact with it.
When you complete the game, you will earn this achievement. The fastest way to earn this is by going downstairs immediately after waking up and eating breakfast with your family. Afterwards, you can use the clock found in the living room to skip time until it is night. Once it is night, you simply need to go to sleep in the room where you started the game.
You must activate all six of the daydreams to earn this achievement. If you would like to know how you can activate them, then navigate to the Daydream section of the guide.
You can earn this achievement by interacting with the umbrella that is located on the side of the home. This is the easiest achievement to get since you can earn it at any time.
Closet Monster Daydream [1/6]
This daydream is activated by entering the closet upstairs that is next to the stairs. To enter this closet, you must first grab the key that can be found in the room with the computer and a balcony.
Jellyfish Daydream [2/6]
You can activate this daydream by interacting with the jellyfish keychain that can be located in the laundry room. Once the memory is activated, a small cutscene will play and you will resume playing outside after you read all the dialog.
Flower Daydream [3/6]
When you interact with one of the bushes outside the home, you are given a prompt that says, "Maybe there should be more flowers," as well as two choices. If you answer yes, then the daydream will be activated. However, if you say no, you will never be given the option to see the daydream again unless you restart the game.
Doll Daydream [4/6]
To activate this daydream, you must stand in front of the doll located in the room behind the stairs, which is on the first floor of the home. It'll only take a few seconds for the daydream to be activated and you don't even need to be looking at the doll.
Cat Daydream [5/6]
This daydream can be activated by grabbing the key found in the room with the doll. After grabbing the key, you need to enter the door that was once locked on the first floor next to the bathroom. After entering the door, you need to talk to the cat to activate the daydream.
Flood Daydream [6/6]
This daydream only occurs in the afternoon while your mother is out shopping. To consistently trigger this daydream, you merely need to wait in the living room in the afternoon.
Piano Sheet Music Conversation
If you play the sheet music found in a drawer next to the piano, you will have a small conversation with your grandmother. Another cool fact is that the sheet music contains doodles of both Kamen Rider and Ultraman.
Here's a video demonstrating how to play the sheet music:
Voltage Tower Monster
If you talk to your brother while your mother is out shopping, he will mention that he had a dream where he was chased by voltage tower monsters. After this dialog is finished, one of the voltage tower monsters can be seen walking nearby the home.
Sometime in the afternoon, a cutscene will play where your neighbor visits and shares some of their grapes with you. While they are visiting, you also create a large teru teru bozu with them.
I have played the game a few times and it appears that you can only get the neighbor to visit if you play the game with days that are 40 minutes or longer. I'm not entirely sure how this event is activated since it seems random.
Outer Railing Dialog
If you walk along the outer railing upstairs and reach the wall, you will receive a dialog referring to what you just did.
If you bring the umbrella inside the house and bring it near your grandmother, she will tell you to not open the umbrella inside. However, nothing else will happen if you continue to use the umbrella inside.
In the afternoon, while your mother is away, your grandmother will ask you if you want to have some watermelon. If you reply yes, then a small cutscene will play.
This seems to be another event that only occurs on days that are 40 minutes or longer. In addition, you might also need to be in the living room after the flood occurs to get this event to be triggered.
As of the moment that this guide is being created, it is possible for players to go out of bounds with the use of one of two objects. The first object is the blue bucket found outside of the home, which is the preferred object to use. The other object that players can use is a brown basket found in the laundry room. The problem with the brown basket is that it is more difficult to move around than the blue bucket, which is why the blue bucket is the preferred object.
The developer has mentioned that they want to remove the blue bucket in the next update, so it might not be around for long. However, they might prevent the player from colliding with the objects rather than removing them altogether, but we'll need to wait and see.
Demonstration & Exploration
The video above demonstrates how you can get out of bounds yourself. While wondering outside of the boundaries, you can see some interesting stuff. You want to make sure that your character is crouching and that you are towards the back of the bucket when you pick it up. After you are floating, the more you move your camera up, the faster you go. However, if you look too far up, you will fall off of the bucket.
When out of bounds, you will notice that the neighbor character is waiting to be used for its cutscene. You can also look inside the box he is holding and see the grapes inside.
You can also see the voltage tower while out of bounds and it is walking even though it is not being used in a cutscene.
You can see the cat daydream area, but you cannot enter the location unless you use the bucket again to get inside. You can also see the traffic light used in the introduction cutscene nearby.
There is a home model constantly used in the background of the map and it appears to resemble the home found in Inaka Project.
There's some more details to see out of bounds, but those are the main ones.